Biomedical Engineering Reference
In-Depth Information
developmentsintheutilizationofnanoceramicmatricesinbonetis-
sue engineering.
4.2 Bioceramics
The word “ceramic” can be traced back to the Greek term
keramos
,
meaning “a potter” or “pottery.”
Keramos
, in turn, is related to an
older Sanskrit root meaning “to burn.” Thus the early Greeks used
thetermtomean“burnedstuff”or“burnedearth”whenreferringto
productsobtainedthroughtheactionoffireuponearthymaterials.
4
Ceramics is defined in the
Encyclopedia Britannica
as “objects cre-
ated from such naturally occurring raw materials as clay miner-
als and quartz sand, by shaping the material and then hardening it
by firing at high temperatures to make the object stronger, harder,
and less permeable to fluids.” This broad classification includes
structuralclayproducts,whitewares,refractories,glasses,abrasives,
cements, and advanced ceramics, which are further divided into
more specific classes, from dinnerware to the National Aeronautics
and Space Administration's (NASA's) reusable, lightweight ceramic
tile for its space shuttle program. Bioceramics is a class of advanced
ceramics that is defined as ceramic products or components
employed in medical and dental applications, mainly as implants
and replacements. It is biocompatible and can be inert, bioactive,
and degradable in a physiological environment, which makes it an
ideal biomaterial. However, it is brittle, with poor tensile strength,
which makes it unsuitable for load-bearing applications. Materials
that are classified as bioceramics include alumina, zirconia, calcium
phosphates, silica-based glasses or glass ceramics, and pyrolytic
carbons.
Calcium phosphates include tricalcium phosphates (TCPs),
hydroxyapatite (HA), and tetracalcium phosphates. HA found in
bone is a poorly crystalline, nonstochiometric apatite formed by
nanosized needle-like crystals. Unlike tetracalcium phosphates and
TCPs, HA does not break down under physiological conditions. In
fact, it is thermodynamically stable at physiological pH and actively
takes part in bone bonding, forming strong chemical bonds with
surrounding bone. This property has been exploited for rapid bone
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